This invention relates to downflow furnace assemblies, and more particularly to the combustible floor base of such an assembly and a method of constructing combustible floor bases.
Downflow furnace assemblies are frequently used to heat homes and other buildings. Such an assembly may comprise, generally, a return air plenum located at the top of the assembly for receiving air from the rooms of the building, a fan to cause the air to flow downward through the assembly, a furnace positioned below the return air plenum where the air can be heated by, as examples, electric resistance heat or a gas fueled burner, and a lower plenum positioned below the furnace for receiving the relatively warm air from the furnace and directing the air toward a plurality of room air ducts which guide the heated air to the individual rooms of building. In addition, in many instances the assembly will include the evaporator coil of an air conditioning unit. The evaporator coil, which can be used to cool air flowing through the assembly, is usually placed in an evaporator coil casing which is positioned above the lower plenum and below the furnace. Use of an evaporator coil in this manner permits both central heating and central air conditioning of the building with only one network of air ducts.
Normally, the room air ducts are located in the space underneath the floor of the building, the furnace is located above the floor, and the lower plenum extends through the floor to connect the furnace with the room air ducts. In many buildings the floor is constructed of combustible material such as wood. When the lower plenum of a downflow furnace assembly extends through such a floor, it is desirable to eliminate the transfer of heat from the assembly, and especially the lower plenum, to the floor. Typically, this is done by the use of a combustible floor base.
Commonly, a combustible floor base includes a pair of side rails and a pair of cross rails. Usually, the rails are fashioned by die pressing metal sheets. Then the ends of the rails are spot welded together to form a generally rectangular base. The rails are shaped so that the floor base can be used with suitable insulating material to provide a thermally insulating frame for the lower plenum for preventing the transfer of heat from the lower plenum to the floor. After the rails are shaped, separate pieces of metal are spot welded to the rails perpendicular thereto, forming spacing tabs or flanges. These flanges cooperate with the edge of the floor to maintain a predetermined distance between the lower plenum and the floor, further insulating the floor from the plenum.
As may be expected, a variety of sizes of downflow furnace assemblies are available, In particular, furnaces and evaporator coil casings come in a wide range of widths and depths, with the size of the lower plenum of the assembly usually matched to fit either the furnace or the evaporator coil casing. Heretofore, different types of floor bases were constructed for each size assembly. That is, combustible floor bases have not been designed or manufactured so that a single base might be used with a number of different sizes of downflow furnace assemblies. This has several disadvantages. First, the multiplicity of types of floor bases increases the complexity of the manufacture of floor bases by increasing the number of different parts involved in the manufacturing process. Second, the fact that different floor bases are designed for different assemblies requires, naturally, that, when a downflow furnace assembly is installed, the specific floor base that is adapted for use with that assembly must be available. Frequently, this is not the case, resulting in a waste of time in obtaining the correct type of floor base.
Bases or frames that may be adjusted to a variety of sizes are, of course, well known. For example, adjustable bed frames are described in U.S. Pat. Nos. 3,775,783; 3,781,930; and 3,871,039. These patents appear to be the most relevant prior art due to the fact that they disclose frames which may be adjusted to a number of different widths. As discussed below, this feature is incorporated into the present invention. The present invention, though, uses adjustable bases in a downflow furnace assembly, and this use of adjustable bases is not disclosed or suggested by the above-mentioned patents. In addition, the adjustable base of the present invention includes integral spacing flanges which cooperate with the edge of a floor to keep the lower plenum of a downflow furnace assembly at a preset distance from the floor. The frames shown in the above-named patents do not have such flanges, and this also distinguishes the present invention from the disclosures of these patents. Moreover, in a preferred embodiment, the floor base of the present invention includes joiner members so that the cross rails can be joined to the side rails at any one of a number of positions. By changing the position at which a cross rail is joined to the side rails, the depth of the floor base can be varied. Thus, the floor base of the present invention is adjustable both widthwise and lengthwise, whereas only the widths of the frames disclosed in the above-identified patents are adjustable, and this is another distinction between these patents and the present invention. Furthermore, because, among other reasons, the frames shown in the above-named patents have neither the integral spacing flanges nor the joiner members discussed above, these patents do not suggest the method of constructing combustible floor frames disclosed herein.